The present invention relates generally to apparatus and methods for supporting vapor-liquid contact devices such as structured packing in columns in which mass transfer and/or heat exchange processes occur and to apparatus and methods for collecting liquid after it exits the vapor-liquid contact devices and redistributing it to other vapor-liquid contact devices.
Random and structured packing elements are used in mass transfer or heat exchange columns to facilitate contact between fluid streams flowing within the column. The packing elements generally improve the mass transfer or heat exchange by providing surfaces onto which the fluid streams are able to spread to increase the area of contact between the ascending and descending fluid streams. The packing elements are generally arranged in a bed which fills the cross section of the column and has a preselected depth or height.
Horizontally-extending supports, typically referred to as support plates, are used to support the bed of packing elements within the column. The support plates must have a high percentage of open area to minimize any restriction to the countercurrent flow of rising vapor and descending liquid. A variety of support plate configurations are used, such as open grid type structures commonly used to support structured packings and corrugated structures used with random packings. The support plates are typically supported by a support ring fixed to an inner surface of the shell of the column and, in larger diameter columns, liquid collection and distribution devices in the form of beams or trusses span the column cross section at one or more spaced-apart locations to provide additional support for the support plates.
In columns with multiple beds of packing elements, liquid exiting one bed is normally collected and redistributed to an underlying bed. This collection and redistribution of the liquid is necessary to correct any liquid flow irregularities present in the liquid exiting from each packing bed before that liquid is introduced into an underlying packing bed. These liquid flow irregularities are generally undesirable because they impede the desired uniform vapor-liquid interaction within the packing bed. Normally, a liquid collector plate is positioned under the overlying packing bed to collect the exiting liquid and feed it to a liquid distributor which is spaced below the collector plate and above the underlying packing bed. The liquid distributor then redistributes the liquid to the underlying packing bed. Alternatively, combined collectors and distributors are used to collect and redistribute the exiting liquid.
The liquid collection and distribution devices that support the packing beds, as well as the liquid collector and distributors associated with the packing beds, occupy a portion of the height of the column which might otherwise be used for mass transfer or heat exchange purposes. In the design of new columns, additional column height may be provided to accommodate these components so that the desired mass transfer or heat exchange within the column can be achieved, but the additional height increases the materials cost for the column. In the case of a revamp of an existing column, the space occupied by these components limits the mass transfer or heat exchange that can be achieved within the column.
A need thus exists for improvements in the support of packing beds and the collection and redistribution of liquid between such beds.